Carbide 3D offers 2 VFD spindle options:
- 65mm VFD air-cooled w/ ER-16 (the previous iteration had an ER-11 collet system)
- 80mm VFD water-cooled w/ ER-20
If you can translate time into money, then you should get the 80mm VFD which will have a greater material removal rate.
If you have a need for 1/2" tooling, then you should get the 80mm VFD. Collets and nuts are a consumable, so I wouldn’t consider having a set of them as a serious aspect and there is no real reason to prefer the smaller ER-11 over a larger size.
Otherwise, the 65mm VFD is at the sweet spot of value and convenience.
To throw something out into left-field, I actually use a 220V spindle:
(albeit w/ a 110–220V step-up transformer)
and have a spare mount — if this interests you, let me know once you’ve placed your order and I’ll ship you my spare and a flat dust plate w/ 2.5" hose adapter which a Sweepy bottom fits on (you’ll just need to source some hardware). The Mafell comes w/ a 6mm collet stock, and they have 1/8" and 1/4" collets, and it further takes 8mm shank tooling, no collet necessary which is pretty convenient now that we have a new line of tooling in that shank size: